This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-58972 filed on Mar. 2, 2001.
1. Field of the Invention
The present invention relates to an evaporative emission control apparatus for treating fuel vapor evaporated within a fuel tank connected to an internal combustion engine so that the vapor is not released to the atmosphere.
2. Description of Related Art
In general, a vehicle evaporative emission control apparatus is provided to an internal combustion engine in order to prevent fuel vapor evaporated within the fuel tank from being released to the atmosphere. In this apparatus, a charcoal canister (hereafter, canister) is provided as a fuel vapor adsorbing means. The fuel vapor evaporated in the fuel tank is temporarily adsorbed by an adsorbent such as activated charcoal powder within the canister. When the inside of an air intake pipe is negatively pressurized during engine operation, outside air is drawn into and passes through the canister to remove the adsorbed fuel vapor from the adsorbent. Then, the drawn air and the removed fuel vapor are fed into combustion chambers of cylinders through the air intake pipe and combusted.
In recent years, however, vehicles with gasoline-injection engines have increased and gasoline-injection engines are being operated at high air-fuel ratios which are, from a theoretical point of view, lean fuel mixtures. In the gasoline-injection engine, the negative intake pressure tends to decrease in accordance with an increase in the air-fuel ratio, that is, in accordance with using a lean mixture. Therefore, it is difficult to ensure the predetermined intake negative pressure for purging the fuel vapor.
Furthermore, vehicles utilizing hybrid driving technology (i.e. xe2x80x9chybridsxe2x80x9d) are increasing. The internal combustion engines of these vehicles boast improved fuel economy with an increase in combustion efficiency. These engines are driven at high speeds and in a highly loaded and maximized state in which a throttle valve is largely opened. This causes pressure variations within the intake system. Therefore, similar to the gasoline-injection engines on non-hybrid vehicles, it is difficult to ensure a predetermined intake negative pressure for purging the fuel vapor.
To solve the above problem, in U.S. Pat. No. 5,975,062, an electric air pump operated by an electric control unit is provided on a purge pipe communicating with a canister and an air intake pipe of an internal combustion engine. Accordingly, even when the negative intake pressure of the engine is low, purging air including fuel vapor removed from the canister is forcefully drawn and fed into the air intake pipe by operation of the electric air pump.
In the above electric air pump, however, it is necessary to prevent fuel vapor from leaking into the motor and to the atmosphere from a sealing portion around a shaft that connects the air pump and the motor. Further, since this electric air pump uses an air-fuel mixture, an explosion may occur if the fuel vapor leaks into the motor and is ignited due to sparks within or from the motor. Therefore, it is necessary to use a motor having an expensive explosion-resistant construction, such as a brushless motor, to prevent an explosion.
The present invention is made in view of the above problem, and it is an object to provide an evaporative emission control apparatus in which electric power consumption of a pump is reduced, the pump being used as a drawing means for removing fuel vapor from a fuel vapor adsorbing means such as a canister and for purging the fuel vapor. Also, leakage of the fuel vapor form the pump, due to pump damage, is eliminated which will increase safety and reduce air pollution. This is accomplished without necessitating a motor having an explosion-resistant construction. Further, a purge amount is easily controlled. It is another object to provide an evaporative emission control apparatus that can diagnose problems in a system without providing an optional problem checking system.
According to one embodiment of the present invention, an evaporative emission control apparatus is provided as a double-acting diaphragm pump used as a drawing means for drawing fuel vapor. In this pump, a chamber is provided on each side of a diaphragm and each is used as a pump chamber. Also, at each end of the pump, two check valves are utilized to control fluid flow into and from the pump chambers. Therefore, the pump can restrict breathing noises from being released outside the pump and also, discharge pressure surges can be reduced. Further, an amount of fluid discharged from the pump can be increased.
The evaporative emission control apparatus of the present invention is suitably used on an internal combustion engine mounted in a vehicle and the like. In this case, an end of a purge pipe is connected to an air intake pipe of the engine, so that combustion chambers in the engine are suitably used as a fuel vapor treating means.
In an embodiment of the evaporative emission control apparatus of the present invention, an actuating means of the double-acting diaphragm pump, a moving core for driving the diaphragm, and a solenoid coil for reciprocating the moving core, and the like, are provided in a pump housing that is hermetically integrated with a pump body. This prevents any pump portion from communicating outside of the pump, for instance, in other types of pumps that may use abrasion of sliding sealing surfaces. Accordingly, the fuel vapor is restricted from leaking outside of the actuating means. The solenoid coil generates electromagnetic power when AC voltage or pulse voltage is applied which causes the moving core to reciprocate. Therefore, power utilization (efficiency) is increased as compared to a case in which rotation is transformed into reciprocation. Additionally, there is no pump portion generating sparks. Therefore, an explosion will not occur even if fuel vapor leaks into the actuating means. Further, since its structure is simple, manufacturing costs are reduced.
The solenoid coil and the like are used as the actuating means of the double-acting diaphragm pump. A discharging amount discharged from the double-acting diaphragm pump per unit time is changed by controlling at least one of voltage, current and frequency supplied to the solenoid coil. Therefore, a purging amount of the fuel vapor, purged from the fuel vapor adsorbing means, can be easily controlled. Further, when the moving core is made of a permanent magnet, the diaphragm may be lifted to its maximum height, thereby increasing the discharge amount.
Check valves, which are automatically opened/closed by a pressure difference between an upstream side and a downstream side of the check valves, are provided at both inlet ports and outlet ports of two pump chambers of the double-acting diaphragm pump and function as pumps themselves. Reed valves can be used in place of the check valves. Also, reed valves can be provided on valve bodies of the check valves. These reed-type check valves are shaped to be open when a pressure difference does not exist between the upstream side and the downstream side which occurs when the pump stops. Therefore, the double-acting diaphragm pump fluidly communicates internally. Accordingly, it is possible to leak test an entire system of the evaporative emission control apparatus including the inside of the pump. A leak test checks the xe2x80x9cleak-tightnessxe2x80x9d of the pump system. Alternatively, a bypass pipe for connecting an upstream side purge pipe of the pump and at least one of two pump chambers is provided to leak test the system. Further, an open/close valve is provided between the pump and the fuel vapor adsorbing means.
In an embodiment of the evaporative emission control apparatus of the present invention, in order to leak-check the system, an open/close valve is provided at an air intake side of the fuel vapor adsorbing means. Further, a pressure detecting means is provided to detect pressure in the fuel vapor adsorbing means, a fuel vapor-generating source connected to the fuel vapor adsorbing means, and the double-acting diaphragm pump. In this case, a general canister open/close valve may be used for the open/close valve provided at the air intake side. Also, a general pressure sensor provided in a fuel tank and the like are used as the pressure detecting means. Therefore, it may be unnecessary to provide optional valves and pressure sensors for the leak test.
In another embodiment of the present invention, a diaphragm pump does not have to be of the double-acting type. Therefore, it is yet another object to provide a diaphragm pump that is not of the double-acting type. A single-acting diaphragm pump is an example of a non double-acting diaphragm pump.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.